Stream : river a. river : sea b. plains : sea c. sea : river d. mountain : plains

A. River : Sea

A river is a larger stream. So note.

1) They have to be the same (water => water).

2) It must go from smaller to larger.

River to Sea is your best choice, for they both have to do with water (#1), and goes from a smaller body of water to a larger body of water (#2).

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